Hot melt adhesives (HMAs) are 100% non-volatile solid thermoplastics. During application, a hot melt adhesive is applied to at least one of the substrates to be bonded at an elevated temperature in a molten state, brought into contact with the other substrate(s) and is then solidify upon cooling. Subsequently it forms a strong bond between these substrates. The most common applications for hot melt adhesives include case and carton sealing, binding of non-woven construction and spine, lamination and bookbinding. A typical hot melt adhesive formulation is composed of base polymer(s), diluent wax(es) or oil(s), tackifier(s), stabilizers and optional filler(s). Combinations of different raw materials are used based on different technical requirements for different application fields. For example a good adhesive for bookbinding should have a proper viscosity for processing, be flexible for multiple flipping, set fast to allow clean trimming, have a long open time to accept cover, bond well to various paper stocks, and have a wide operation temperature window for extreme high and low temperature application fields.
Compared to other technical approaches, hot melt adhesives are widely used in bookbinding because of their production efficiency and cost benefit. The most commonly used base polymers for hot melt adhesives in bookbinding applications are ethylenevinylacetate copolymers (EVAs) and styrenic block copolymers (SBC). EVA-based hot melt adhesives are employed in high speed operations due to their fast setting, lower cost and easy handling, and because EVA is one of the most versatile base polymers. However, EVA copolymers generally have poor temperature resistance, because in order to achieve enough flexibility, EVAs having a high vinylacetate (VA) content are required, which have lower softening points. Moreover, the polar VA group can lead to an inferior thermal stability of the copolymer at high temperatures in the presence of air, which can lead to the appearance of char, skin or gel. Also styrenic block copolymers have been widely employed in the state of art in hot melt adhesive formulations in order to achieve good performance for book binding.
U.S. Pat. No. 4,722,650 discloses a case for a hard cover book and a process for the production of a book case which employ a composition which inter alia comprises a specific A-B-A block or A-B-A-B-A-B multi-block styrene-butadiene copolymer.
U.S. Pat. No. 4,942,195 discloses hot melt adhesive compositions suitable for bookbinding application which inter alia contain specific Styrene-Isoprene-Styrene (SIS)/Styrene-Butadiene-Styrene (SBS) block copolymers. The compositions can contain Fischer-Tropsch waxes.
Compared to styrenic block copolymers and EVA copolymers, polyolefins have better thermal stability, wider operation temperature window and lighter odor at high temperature. Metallocene-catalyzed polyolefins have been used for packaging and show a set speed and adhesion as good as the conventional EVA products.
U.S. Pat. No. 6,582,829 B1 discloses a hot melt adhesive compositions comprising at least one homogeneous linear or substantially linear ethylene/α-olefin interpolymer and at least one block copolymer and at least one tackifying resin for paper packaging and bookbinding applications.
WO 01/34719 A1 also discloses a hot melt adhesive for use in bookbinding comprising at least one homogeneous linear or substantially linear ethylene/α-olefin interpolymer and at least one tackifying resin and optionally inter alia a block copolymer.